docs: def get_restricted_sites(self, request):
          """
          The sites on which the user has permission on.
  
          To return the permissions, the method check for the ``get_sites``
          method on the user instance (e.g.: ``return request.user.get_sites()``)
          which must return the queryset of enabled sites.
          If the attribute does not exists, the user is considered enabled
          for all the websites.
  
          :param request: current request
          :return: boolean or a queryset of available sites
          """
          try:
              return request.user.get_sites()
          except AttributeError:  # pragma: no cover
              return Site.objects.none()